Telephone system



April 18, 1933- N. H. sAUNDERs Er Al. 1,904,933

TELEPHONE SYSTEM Narman H.5aun sr's laranas ELC/max April 18, 1933.

.['ELEPHONE SYSTEM Filed Aug. 24, 19151 2 SheetS-Sheel 2 Clarins: E. Ln'max ,sa make such systems more eiicient an Patented Apr. 178, 1933 UNITED STA-res FAn-.1u'1r om@ NonivrAlxr 1r. sAUNnEnsbr CHICAGQAND "CLARENCE n. LOMAX, oF OAK PARK,

Immers, Assrenons, BY Mnsnn ASSIGNMENTS, To ASSOCIATED. ELECTRIC LABO-` RATONES, inc on cHrcAso, ILLrNors, A CORPORATION AoF DELAWARE TELEPHONE SYSTEM Applicationled August 24, 1931., Serial No. 558,912;

This invention relates in general to telephone systems', particularly telephone systems comprising a manual central `oliice or switching center and a number 'oi' relatively 5 small automatic oiiices, and it is concerned primarily with circuits and apparatus for interconnecting the otlices of such systems.

The trailic conditions and geographical location of the oiiices of a multi-office system of the type above-referred to occasionally make it desirable to interconnect the various oliices by one or .more trunk lines which extend from the switching center through allot the automatic offices. Each `automatic office is provided withswitching apparatus associated directly with the trunk line to enable the operatorv atv the switching centerA to select anyone of the offices in which the'line of a wanted `'subscriber'is accessible.V 2o Trunk lines of this type may be arran 'ed for handling calls from anyjautomatioo ce to the switching center in *addition to the calls from the switching center to the various automatic oilices. `In this case 1t is necessary to make provisions for busying the trunk line in the various offices whenever the-same is in use in aconnection. It is also desirable that the trunk line besan ranged for use in connectingsubscrbers in `3o different ones of the automatic offices.

The system chosen to illustrate the present inventionis one in which the automatic oliices employ switching equipment of the general type disclosed in United States Pa*- ent No. 1,772,690, granted August` l2, 1930 to N. H. Saunders. Each automatic office is designated by a particular olice digit which identiies this office.` Two oliices have been shown inthe drawings, one designated by the digit Sand the other by the digit 5.

These ollioes will be referred to hereinafter as office A and office B,re`spectively.

The provision of new and" improved circuitsand apparatus for use in systemsot e5 the above type is the mainv object of. the

present invention. The various features of the invention relate to improvements in Vcontrol circuits, supervisory circuits, and associated switching' apparatus tendin to liable. Thesefeatures together with theopf eration of the system embodying theV invention will be described in detail, reference.

being "had to. ,the accompanying drawings comprisingFlgs. l and2.4 .These drawings showV by `means of the usual `circuit. diagrams a sullicient amount of equipmentin a multi-oiiice system embodying theinvention to permit the invention to be readily ex@ plained andunderstood. Fig; lshows the apparatus vassociatedrlwith an interoliice trunk line at a switchingv center and also a part of the apparatus at an automatic oliice. Fig. 2 shows the trunkapparatus and exchangeswitching apparatus at anotherautomatic oiiice. In order to be best understood,

vthe udrawings should be placed `with Fig. 2 n to theV right 'of'FigV l and with correspondf' apparatus shown in Fig. 2 vwhichis located f in office' A. A` second branch of thetrunk extends to the switching apparatus SA shown' below Vthe lower broken line in- Fig. o

l which is located-in office B. There may be anyynuinber'of otherolices connected in the trunk'line in the manner shown `and in each case the equipmentprovided will be substantially the sameas that shown in the present drawings. o Y Y f VThe trunk relay group in which the trunk line T terminates is provided 'with a jack-J by means oi whichthe operator completes connection to and from -the trunk.

Connections are completed by means of-a manual cord circuit C which may be ofany suitable type and which is shown only in skeleton form. A calling device DV common to all'trunks at the manualoperators! posi# tion may be'connected to the trunkline by means Vof the key K.

The switching Vapparatus `SA shown. at the bottom of Fig. 1 is connected to the trunk line at the office B. Only the essential parts of the switching apparatus SA have been shown as this apparatus is exactly the same as switching apparatus SA1 shown in Fig. 2, except tory the wiring oit the bank contacts of rthe rotary switch. Relays and contacts have been designated similarly to corresponding relays and contactsof the equipment shown in Fig. 2 tor convenience in describing the operation of the circuits. For example, relay 21 in Fig. 1 corresponds to relay 121' in Fig. 2, etc.

Referring now to Fig. 2 the switching apparatus SA1 is associated with the trunk line T at ofice A. This apparatus consists of a group oit relays and a rotary switch which is directively controlled over the trunk. Lineswitch LS is adapted to bre-associated individually with the branch ot the trunk T and has access to local connectors in oilice A of which one, connector C, is shown in skeleton form. Lineswitch LS1 is a lineswitchA similar to lineswitch LS and is individual to the subscribers line S. This lineswitch and other similar lineswitches have access to the connectors of the automatic otice. The connector has access to trunk line T and other similar trunk lines, and also to the various subscribers lines which terminate in this oilice. The lineswitches and connector shown in the present application are similar to those shown in the Saunders'patent previl ously referred to.

Having briefly described the invention and the system embodying the same, the operations involved in establishing various connections in the system will now be described in detail. The establishment of a connection from the manual switching center to the subscribers station S in olice A will be considered first.

Assuming that a call from a distance point is received by the operator at the switching center, the operator will answer this call by means of a cord circuit, such as cord circuit O, and on determiningY that the call is for the subscriber S, will insert the calling plug P ofthe cord circuit into the vjack J of an idle trunk line. Upon the insertion et the plug into the jack a circuit will be closed for relay 9 by way of the sleeve of the jack plug and that relay will operate. Relay 9 in operating completes the circuit at contacts 18 for supervisory lamp L1, disconnects relay 8 from the trunk line at contacts 16, and connects relay 7 to the trunk line at contacts 17. A circuit may now be traced from ground, winding of relay 7, contacts 11 and 17, lett-hand windings ot repeating coil R, trunk conductors V1 and 2 in parallel, branch conductors 3 Vand i in parallel, contacts 1341- and 139, contacts 1110 and 1/15, windings of impedance I, contacts 148 and V159, relay 129 to battery. A parallel circuit may be traced for relay 7 including branch conductors 5 and 6 in parallel, contacts 34 and 39, contacts l0 and 45, impedance l', relay 29 and battery. Other similarparallel circuits will eXiSt in all other oliices which are connected to the trunk lin-e T. Relay 7, and relay 129 and the corresponding impulse relays in the other offices will operate over the above circuits. Relay 7 opens a point inthe circuit of supervisory lamp L1 at contacts 13. Relay 129 completes a circuit for relay 130 at contacts 163 and similar circuits are completed by the correspondingy relays in the other oiiices. Relay 'on operating applies ground by way or" vcontacts and 146 to conductor 173 to mark the trunk line busy to the connectors in oliice A. A point in the release circuit is opened at contacts 166, the inipulsing circuit for the rotary switch is prepared at contacts 167, vandV a point in the switching circuit is prepared at contacts 168.

After having-established connection with the trunk line the operator at the switching center will actuate key thereby disconnect-` ing relay 7 from the trunk line at contacts 11 and substituting therefor ground through impulse contacts 10 of the calling device by the operation of contacts 12. Relay 7 will restore and complete the circuit of lamp L1, but the impulse relays corresponding toV relay 129 at various oliices will now be operated over the circuit extending` to ground through the 'impulse contacts o'i' the dial.

As previously stated the ottico Afis designated by the digit 3, office Bis designated by the digit 5. Other etlices will hayejdesig-L nations which kdistinguish from th-e two mentioned, but in every case the operation will be in general the same and need not be described in detail. The calling operatorwill accordingly dial the digit 3, thereby interrupting the previously traced circuit ot the impulse relays three times. The impulse relay in each office willrespond to the impulses and operate the associated rotary switch as will be described for relay 129 of switching apparatus SAL Relay 129 upon restoring for each impulse completes a circuit by way of contacts 162 and 167, winding of relay 131, rotary magnet 132 to battery. 131 and the magnet operate, the latter advancing wiper 178 ot the rotary switch one step. Relay 131 is slow-to-release and remains operated throughout the series of im- L.

pulses. Relay 130 is also slow-to-release and remains operated when its circuit is momentarily opened during impulsing at contacts 163. The rotary magnet thus advances the wiper 178 step-by-step until the third contact, that is, contact 17 O is reached. Shortly alterA the lastrimpulse of the seriesrelay 131 will release, thereby closing a circuit by way of contacts 168, 169, wiper 17 8, Contact 170,

Relay lower winding of relaj,7 121 to battery. The .335

release of the relays'corresponding to relay J' olice.

which are different than the one just described, since the other offices are designated by digits other than 3 and the rotary switch banks are accordingly wired in a dierent manner. Mre specii cally, in the other of-V Vfices circuits will be closed for the relays corresponding to relay 126 and this relay will operate to disconnect the normally connected impulse relay from the trunk line as will be explained subsequently.

Referring now to the operation of switching apparatus SAl upon the completion of Vthe dialling of the office digit, relay 121 will operate over the circuit previously traced and at contacts 135and 138 will extend the trunk conductors through to lineswitch LS. 1t will be recalled that ground through the impulse contacts of the calling device is connected to the two trunk conductors, and this ground extending by way of contacts 103 and 104, relay 101 to' battery operates relay 101. A circuit is thereby closed atconl' tacts 109 for the pull-'down winding of linesWitch LS. The plunger of the lineswitch is accordinglyforced into the banks closing contacts 179-182 which extends the connection through to connector C. The impulse and release relays ofthe connectoroperate in the usual way and return a hold-V ing ground over release V.trunk conductor 106. This ground'V energizes the holding winding of the magnet 102 of the lineswitch VLS and prevents the release of the lineswitch upon the release of relay 101 which is brought about by the opening of contacts'- 103 and 104 Vupon the operation of the plunger. Holding ground extends'back by way of conductor 176, contacts142 and 137, through the upper winding ofY relay 121 and maintains this relay in'operated condition. The trunk conductors have been disconnected from impulse relay 129 at contacts 134 and 139 by the switching operations just described and relay 129 releases. The circuit of relay 130 is opened at contacts 163 and relay 130 restores and completes a circuit for release magnet 133 at contacts 166. The release circuit includes oit-normal contactsV 118 which closed upon the first step of the rotary switch. The rotary switch is accordingly restored to normal by the operation of the` release magnet and upon reaching normal condition, off-normal contactsV 118 are again opened and the release magnet accordingly restores.

VThe calling operator-now dials the number of the called subscriber in the called t' key K to normal again connecting. relay 7v n subscriber hangs u Connector C is stepped to the con i tacts of the called line ina well known inanto thetrunk line. The called subscriber will be signalledautomatically inthe usual manner and relay 7 will be operated in series withthe impulse relay ofthe connector during: this interval. When Vthe called sub:-

pervisory lamp L1, `which glows toV givel Y answering supervision.

at'the'end of the con* versation, relay :10 will` again operate and openthe circuit" for lamp L1, which'willbe extinguished-to indicate to the operator that theV connection. is to` be taken down.A lThe operator Will accordingly withdraw the plug from the jack, there'byfreleasing` relay 109 `which disconnects relay 107 from the trunk.

The circuit of the-impulse yrelay of the coiiv nector is accordingly opened and `that relay When the called Y releases and the connector restores to'normal in the usual manner. x Y

The apparatus` involved-"in other -oiiices l than the one called upon the dialling of Vthe [irst or oiiice designating digit will now be described. In this case it will be assumed that Y a` subscriber at -oiiice B is-called in which case the oliice digit 5will be dialled by l the operator. The rotaryswitches in the various oces will be setion thefth lcontact j of their respective banksyin lthe manner` pre- `viously described forrfcalls tofoflicel A. i Re-l lay 21 of the switching.f,apparatus-'SAinl oiiceV B will operate and extend the connection throughV to theV associated (lineswitch which will, operate i as described' forv lineswitch LS; Referring now toFig. 2 upon the release of relay 131 following the last impulse of the series, a circuit will be completed by way of contacts 168 and 169wiper 178, bankcontact '171, contacts 153, winding of relay 126to battery. Relay 126V is pro` vided with a single armature spring to the end of which` a weight is afiixed. The'relay on being energized immediately closes-contacts` 154, thereby' completing an operating circuit for relay 127.. Upon the release Vof relay126, however, thearmature spring will vibrate due to the weight, andvwill intermittently close contacts 154 and 155- until amplitude of vibration `decreases vto a-fpre# determined extent.l VVVlien this point is reached, relay 127 willrestore to normal.VV

The operation of` relay 127. completes a ciri cuit at contacts 156 forV relay 12.5". Relay 125 operates and completes a circuit for relay 123 at contacts 151, completes a-circuit for relay 122 at contacts 152,1 and at contacts 153 opensthe circuit for relay 126, Relay 123 cperatesjand connects busyingground to. conductorV 173 at contacts 1147, disconnects line relay 129 from the trunkfat contacts 148, Yand at contacts 149 connects high re-V sistance relay 104 to the Ytrunk line. VRelay.v

124 may operate momentarily'at:thisjtime although this is of no consequence. Relay 122, whose circuit was closed by the operation of relay 125, is slowto-operate and, after lan interval, operates and disconnects the trunk conductors from relay 124 at contacts 140 and 145. Relay 126 deenergizes upon the opening ci its circuit at contacts 153 and the armature vibrates as previously explained. Holding relay 127 remains operated for a predetermined interval which isrdetermined by the adjustment of the weighted spring. vAn interval oflitteen seconds is ordinarily suiiicient in the case where three additional digits must be dialled to complete the connection, and it will be as suined in the present case that the relay 127 remains operated for this interval after the opening of the circuit of relay 126. It will be seen from theY foregoing that the trunk conductors willbe entirely clear vat all offices Vother than the-particular one called during this( fifteen second interval. This arrange- Vment increases the operating efficiency of the trunk andy permits lthe use of standard connectors and other apparatus in the various oliices. Inasmucli as the impulse relay of the connector is the only relay connected to the trunk during this period the operation willbe as reliable as if only one oilice were servedby the trunk. At the end or t ie cutoil'` interval, relay127 will restore and open the circuit oi relay 125. Relay will accordinglyrrestore andl open the circuit ot to deenergize and relay 124 will remain operated and maintain the equipment in the position just described'. Impulse relay 129 in the meantime will have released followed by Yrelease of relay and the restoration Vof the rotary switch to normal.

Upon the vrelease of the connection the switching apparatus SA in the called oliice will restore in the manner previously described or callsto ollice A. The high resistance supervisory relays at the various Votlices (relay 124) will also restore. These relays 'will in turn permit the restoration of the relayscorresponding to relay 123, thereby returning all equipment to normal condition.

In the case et a call originating in one of the automatic offices, for example at the suhstation SLior a subscriber in another o'fiice,

the operation will be as follows. They subscriber on initiating a 'call operates lineswitch LS1 which immediately .connects with an idle connector, such as C. Con- .iector C is operated in the usual way to the level in which the trunk lines are accessible and an idle trunk line is accordingly selected. Assuming this selected trunk line to be the trunk line T, a circuit will be completed over the test wiper of the connector, conductor 173, contacts 146, 164, 142, and

136, relay 128 "toV battery. Relay 128 on operating connects ground to vcondiuitors 172 and 174 at contacts 158 and 161, kand at contacts 157 connects ground to trunk conductor 3. A circuit is closed for relay 122 Vat contacts 16()y and the latter relay operates andloclrs to groundat contacts 143. The circuit of relay 123 is accordinglyr opened at contacts142 and this relay releases a short time after the opening of the circuit. The momentary connection of ground to the conductors 172 and 174 effects the operation of ring-cut-ol'l relay in the' connector in the well known manner, and the operation of relay 122 extends the trunk conductors through to conductors 119 and 120 at contacts 141 and 144. A talking connection is thus prepared between thecalling 'subscriber and the operator at the switching center,7

Referring now to the Vapparatus at the` switching center, the momentary connection of ground to conductor 3 causes .the operation of relay 3 of the trunk relay group TR.

rlhis relay closesl a circuitor the line lampA L at contacts 14 and at contacts 15 connects ground to the two trunk conductors in par-v allel. Relay 8` is accordingly'held up over the circuit including contacts 15 yand 16 after the release of relay 123 of the trunk apparatus SAL The line lamp glows to indicate the arrival of the call to the operator. ln ciiices other than the one in which the call originated thel impulse relays are operated by the connection of ground to the trunk conductors and these relays accordingly operate and mark the trunk busy in the banks of a connector at the respective ofices as described in previous connections. The operator on answering sorting the plug P orn the cord circuit C into jack J operates relay 9 which nfan 'ob-V vious manner substitutes relay 7 for re lay 8 in the connection to the trunk. Relay 7 voperates in series with the impulse relays of the switching units at the various otlices and opens the circuit of the supervisory lamp. Relay 8 restores and opens the circuit of the line lamp L and also disconnects the ground fromV the trunk at contacts 15.

In case the call is tor a subscriber in a different system the operator will accordthe call by iii-Y extending to the wanted exchange or system.

It, however, the call is for asubscrib'er in wanted subscriber'will be called'inv exactly the same manner as previously described for calls originating at theswitchmg center,

although in this case since the impulse relay,

at the calling oiiice A sldisconnected from the line there will be no operation of the switching apparatus at that office. The connector at the called oflice will be operated to extend the connection to the called line and the disconnect apparatus at the other offices will function as previously describedv to conf neet the high resistance supervisory7 relays'- called number, and means controlled' by the devices in the Vother offices for clearing the to the trunk.A i

At the termination of the connection, the

called subscriber on hanging up first willv give the operator disconnect supervision in the same manner as for calls originating in the switching center. If the calling subscriber hangs up iirst, the calling connector will restore and open the-previously traced holding circuit for relay 122 which will also restore. Rela 122 will reconnect impulse relay 129 to t e trunk conductors, thereby permitting relay 7 of the trunk relay group TR to operate and give the calling operator the usual disconnect supervision. The `release of the connection in this case will be brought about by the withdrawal of the plug from the jack in the usual manner.

What is claimed is:

l. In a telephone system, a switchingcenter and a plurality of automatic offices serially connected by a trunk line, subscribers lines terminating in saidofices, means at the switching center for transmitting digit impulses representing the number of a called subscribers line over the trunk line', the lirst digit of the number designating theotlice in which the called line is located, a switching device in each oiiice operated responsive to the transmission of the first ydigit of the called number, and means controlledby the devices in the Voiiices other than the one des-V ignated by the digit transmitted for tempo'-A rarily clearing the ltrunk line of all con-` nections in such offices.

2. In a telephone system, a switchingcenter and a plurality ofV automatic oflices serially connected by a trunk line, switchingdevices in said oiiice connected to the trun line in multiple, subscribers lines terminating in said offices, means at the switching center for `transmitting digit impulses corresponding to the number of a called line over the trunk line, means for operating all of 30 said switching devices responsive to 4the iirst digitrof the called number, and means operated under control of said devices for temporarily disconnecting the devices 'from' the trunk line. f

3. In a telephone system, a switching cenally connected by .a trunk line, subscribers lines terminatingrin said ofces, means at theV switching center for transmitting digit im-v pulses corresponding to .the number. of a ter and a plurality 'of automatic oftcesseril i called line over the trunk line, the irst digit of the number designating the .office in which the called line is located, a switchingV device in each oiiice operated responsive-to the first digit of the called number, switch- .ing apparatus ineach office for extending connections to called lines, means controlled bythe switching device in the oice designated bythe digitlcalled for rendering the switching apparatus at that oiiice directively operable' by the remaining digits ofthe Y trunk line of all 'connections' Vror'an interval long enough to 1 ermit the transmission of' said remainingl igits; i 4 4; Inla telephone system, a `plurality ofoiices, a trunk line connecting said oilices,"V

switching devices connected to `the trunk une at yeach oiiice, `means for transmitting atov series of impulses designating one ofsaid Y oiices over the trunk line to operatesaid devices simultaneously, and "means associated I with each device and controlled responsive to the operation thereof for disconnecting the devicesifrom the trunk line.

5.` In a telephone system, a'y plurality offolices connectedby a trunk line, a switching device in eachl oliice connected toV the"- trunk line, means fortransmitting a series, ,Y of impulses designating one of `said oiiicesover the trunk line to operate said devices o simultaneously, and means associated with each device and controlled'responsive to the operation'thereof for temporarily discon-` extending Vfrom the manual olice to all of said automatic oiiices, `switching apparatus in each automatic olice connected to the trunk line,.other switching apparatus 'in each office for extending connections to called lines,

ios

means' at themanual oiiice for transmitting a series of impulsesdesignatingV one of said automatic offices over the trunk line to oper- Y ate theswitching apparatus in 'each'auto- .matic olice, and means responsivev tothe operation of said apparatus for temporarily disconnectingl the same from the trunk line and for renderingV the other switching'japparatus in said one oiiice directively controllable over the trunkVV line. A Y

A7. Ina telephone system, a manualoiiice;

a plurality of automatic offices, a trunk line extending `from the manual oiiice through Y 10oV i all of said automatic oliices, switching .apparatus in each automaticy oliice connected to the trunk line, means at the manual oihce for transmitting a series of impulses designating one of said automatic oiilces over the 8. In a telephone system, two ollices, aV

trunk line extending to said oliices from a remote controlpoint, means at the control point for transmitting an o'lilceselecting digit over the trunk line to operate switching apparatus in both of said oiicessimul-- taneously, meansv at the control point for transmitting line selecting digits lover the trunk line to operate other switching apparatus in the selected oilice, and means controlled by the apparatus in the non-s elected oflice for clearing the trunk line Voi' attachments `during the transmission ofthe oiiice selecting digits to prevent interference with the operation of the apparatus in the selected office.

9. In a telephone system, two oilices, a trunk line extending from a remote control point to said oiiices, means at the control point for transmitting an otlice selecting digit and line selecting digits over the trunk line, switching apparatus at each oliice operated responsive to the oitlce selecting digit, other switching apparatusin the selected oitice operated responsive to the line select- A ing digits, and disconnect apparatus at vthe non-selected apparatus controlled by the yswitching apparatus for clearing the trunk line of attachments in that ollice for a predetermined time to prevent interference with the operation of the apparatus in the selected oiiice.

l0. In a telephone system, a trunk line, a plurality of impulse relays connected to the trunk line, a switching device controlled by each relay, means for simultaneously operating said relays to set the respective devices, and means associated with each device and operatedresponsive tothesetting of the device for disconnecting the associated impulse relay from the trunk line.

. 1l. In a telephone system, a trunk line, a plurality of relays connected to the trunk -line at different points, a .plurality of other relays, a switching device tor each ot said first relays, means for simultaneously operating said first relays over the trunk line to set the respective devices, and means associated with said devices and operated responsive to the setting thereof for disconnecting said first relays from the trunk' line and for connecting said other relays to the trunk line at said different points.

12. In a telephone system, a trunk line, a plurality of relays normally connected to the trunk line at diierent points', a plurality of other relays, aswitching device for each of said tirs relays, means for simultaneously operating said first relays over the trunk line to set the respective devices, and means responsive to the setting of said devices for disconnecting said first relays from the trunk lineV and tor connecting said other relays to the trunk line after a predetermined interval o time.

13, In a telephone system, a trunk line, a plurality of switching devices connected to the trunk line, a non-numerical switch associated with each of said devices, means for simultaneously setting said devices to corresponding positions, and means controlled by the setting ot the devices Jfor disconnecting all oi the devices from the trunk line and 'for connecting the switch associated Vwith a particular one of said devices to the trunlr line.

le. In a telephone system, a two-conductor trunk line, a plurality of relays connected to the trunk line, a switching device associated with each relay, means for simultaneously operating said relays over the two conductors of the trunk line' in ,parallel to set the respectiveswitching devices, and means responsive to the setting'oic said devices 'forY temporarily disconnecting said relays from the trunk line.

l5. In a telephone system, a trunk line extending from onel oiiice to a plurality of other oflices, a line relay and a cut-off relay associated with the trunk line in each of said other oilices, means for seizing the trunk lineat any of said oiiices to extend a connection, means responsive to the seizure of the trunk line at said one otlice for operating-the Y the tirst oliice, a relay connected to the trunk line in each of the other ofces, means controlled by said relays for marking the trunk line busy in the respective offices, means responsive to the seizure of the trunlz line at lla the lirst oillce for operating all of said relays,

and means responsive to the seizure of the trunx line at one of said other oilices for operating said signal and the relays at all et the other oilices except the one at which the trunk line is seized.

17. In a telephone system, a trunk line extending from one office to a plurality of other ollices, a relay connected to the trunk line at each olice, means controlled by said relays for marking` thetrunk line busy in the respective offices, means responsive to the seizure of Vthe trunk linev at the irst office Vwhich the trunk line was seized. ioA

offices, means responsive to the seizure ofl the trunk line at one of said other ofiices for relay at the first office for maintaining the other operated relays in operated condition independent of Control from the office 18. In a telephone system, a manual oflice and a plurality of automatic ofiices serially connected by a trunk line, a calling line in one automatic office, a called line in another I automatic ofiice, an automatic switchat said,

one automatic ofiice directively controlled over the calling line for establishing a con-` nection with the manual ofice over the trunk line, and an automatic switch at said other automatic ofiice directively Vcontrolled from the manual office over said trunk line for extending the connectionto said called line.

19. In a telephone system, an operators switchboard, a plurality of automatic ofiice, a trunk line extending from the switchboard to all of said oflices,'switching apparatus at each oiiice connected to the trunk line, a

- called line in one of said offices, a called line in another of said ofhces, means at said one office for establishing a connection between the calling line and the switchboard via the trunk line, means including the switching apparatus at said another ofiice directively controlled over the trunk line for further extending the connection to said called line, and means including the switching apparatus at the remaining oiiices for clearing the trunk line of all connections while the connection is being extended.

20. In a telephone system, an operators switchboard, a plurality of automatic ofiices, a trunk line extending from the switchboard to all of said offices, a called line in one oflice,

a called line in another ofiice, other lines inv the other oflices, means at said one ofiice for establishing a connection between the calling line and the switchboard -via' the trunk line, means at said another ofiice directively controlled from the switchboard o-ver the trunk line for further extending the connection to the called line, means in said other offices for clearing the trunk line of all connections in such oflices for a predetermined time during the further extension of the connection, and means at each of said offices for marking the trunk line busy at the respective oflices as long as the connection is maintained.

2l. In a telephone system, three offices connected by a trunk, switching devices in the rst vand second offices connected to the` trunk, other switching devices in thel first and second ofhces, means at the third ofiice for transmitting a series of impulses designating either the first or second oiiice over the trunk to set both of the connected switching devices, means controlledY by the device in the oilice designatedffor connecting the other switching device in that ofIice to the trunk, and means controlled by the device at the, non-designated oflice for disconnecting itself from the trunk.

22. In a telephone system, the combination 1 comprising a trunk, switching devices connected to the trunk, automaticswitches, means associated with eachdevice for con,- necting an automatic switch to thextrunk, time vdelaymeans associated with each de-` vice for disconnecting the device from the trunk, means for simultaneously operating said devices, and circuit connections for operating either said connecting means or saidV delay means under control of the associated devices. l f

23. In a telephone system, a two-conductor trunk, a plurality of relays normally connected to the two trunk conductors, a plurality of other relays, a switching deviceassociated with each of said'rst relays, means for operating said first relays overv the two trunk conductors in parallel to set their associated devices, and means-responsive to the setting of the devices for disconnecting said firstrelays from the trunk conductors and for connecting said other relays thereto.

V24. In a telephone system, av trunk a plurality of switching devices connected to the trunk, a non-numerical switch associated with each of saiddevices, other trunks accessible to saidswitches, means for simulta-l the devices for disconnecting the same from Y the trunk line and for connecting the switch associated withafparticular one of said devices to the trunk line, and meansin the switch operated responsive to its connection withithe trunk for effecting a connection be- Y tween the trunk and one of `saidl other trunks.'`

-In witnesswhereof, I hereunto subscrib'eug) v my name this 20th day of August, A. D. 1931. i NORMAN H; SAUNDERVS.

In witness whereof, YI hereunto subscribe my name this'20th day of August, A. I).

CLARENCE LoMAx. 

